In many animals, a phenomenon is often observed in which behavior depends on population density and many individuals within the group synchronize their state of behavior to some extent, and theoretical studies have suggested that this synchronization phenomenon is adaptive for predation avoidance. Moreover, death-feigning behavior (DF) has been observed as an anti-predator strategy in many animals. There are large individual differences in the duration of DF, and the optimal duration of DF often varies depending on the situation. Therefore, although it is expected that prey may synchronize with others around them for an optimal DF duration, there are few experimental studies testing this hypothesis. This study investigated whether DF duration varies with and without other individuals, and whether it synchronized with the DF duration of other individuals, in the red flour beetle